The invention relates to a process chamber in which various processing steps in the manufacture of semiconductors can be carried out in accordance with the preamble of the independent patent claim.
Several processing steps in the manufacture of semiconductors, in particular in the manufacture of integrated semiconductor circuits, take place in such a manner that the wafer (a disc on which a large number of such integrated semiconductor circuits are arranged) is rotated in a process chamber. In addition to this it is often necessary to carry out the individual steps under clean room conditions. In the individual processing steps, in particular media such as liquids (e.g. etching liquids, cleaning fluids, photosensitive resists, developers, etc.), vapours (e.g. metallic vapours or liquid vapours etc.), gases (etching gases, oxygen for oxidation, flushing gases, protective gases, etc.), suspensions (e.g. for the production of passivating layers and other thick film layers), molten polysilicon, electromagnetic waves, ion beams and yet others are applied to or act on the wafer respectively. Several selected processing steps will be briefly mentioned in the following in an exemplary manner which take place in a process chamber in which the wafer is rotated.
For example a photosensitive resist can be applied from a liquid nozzle (or else from a spray can) to the rotating wafer, such as is described for example in U.S. Pat. No. 5,395,803. Alternatively, it is also possible to apply the photosensitive resist to the wafer at rest and then to rotate the latter, as is for example described in U.S. Pat. No. 4,822,639.
As a result of the increased surface tension at the edge of the wafer, slight super-elevations often occur here, which must be removed. This takes place in that a solvent is applied to the rotating wafer in the peripheral region, as is e.g. described in U.S. Pat. No. 4,510,176. This processing step can for example also be combined with the application of the photosensitive resist, which is described for example in U.S. Pat. No. 5,773,083.
In another processing step for example suspensions are applied and passivating layers thereby produced on the wafer. In this, in a manner similar to the photosensitive resist coating, for example liquids with smallest glass or silicon dioxide particles are applied, which then produce the passivating layer. Processing steps of this kind are for example described in U.S. Pat. No. 5,376,176 or in U.S. Pat. No. 5,328,871. In layers produced in this manner a processing step is likewise required in which edge super-elevations are removed (as e.g. described in U.S. Pat. No. 4,732,785).
It is furthermore also possible to produce thin film layers on rotating wafers, e.g. of silicon dioxide, of metals or of carbon (DLC=Diamond-Like Carbon). For this purpose the wafers are coated by means of known procedures such as for example the CVD (Chemical Vapour Deposition) process or the PVD (Physical Vapour Deposition) process. In these processes the homogeneity of the coating of the wafer can be advantageously influenced through the rotation of the wafer, in particular when the wafer rotates very rapidly, e.g. with speeds of rotation up to 16,000 rpm. Methods of this kind are described for example in U.S. Pat. No. 5,630,881.
Furthermore, methods of this kind are also suitable, for example through the application of molten silicon to a rotating plate, to manufacture polycrystalline silicon wafers, in a manner similar to that already described in the production of the xe2x80x9cthickxe2x80x9d layers. This is e.g. described for example in U.S. Pat. No. 4,561,486.
Furthermore, it is also possible to apply liquid or gaseous solvents to a rotating wafer for the removal of coatings, e.g. for the removal of photosensitive resists. This is described e.g. in U.S. Pat. No. 4,749,440 or in U.S. Pat. No. 4,510,176.
Moreover, it is also possible to exploit the rotating wafer for various etching processes. This is advantageous in so far as a homogeneous etching speed is therein achieved over the entire wafer, which can be of importance in particular in order to avoid an under-etching. If for example etching liquid is applied to the rotating wafer from a nozzle, then a homogeneous etching film develops, which is uniformly renewed in a manner which is controlled by the liquid supply. This is described for example in U.S. Pat. Nos. 4,903,717 or 4,350,562. Alternatively, it is also possible to allow the wafer to rotate on a liquid film, as is described in U.S. Pat. No. 4,350,562.
In other etching processes, etching vapours or etching gases are used for the etching of the wafer, as is described for example in U.S. Pat. No. 5,370,741, in U.S. Pat. No. 5,174,853 or in U.S. Pat. No. 5,248,380. The wafer which is exposed to these vapours or gases is likewise rotated during the etching process. In this etching process it is also possible to etch both sides of a wafer at the same time (U.S. Pat. No. 4,857,142). In the so-called xe2x80x9cplasma etchingxe2x80x9d process a gas which is ionised with the help of an electrical field (xe2x80x9cplasmaxe2x80x9d) is used for the etching. This is for example described in U.S. Pat. No. 4,230,515. In all the described etching processes it is advantageous when the wafer is rotated.
Furthermore, it is also possible to carry out ion implantations on rotating wafers. In this the wafer, which rotates with a speed of rotation of about 500-1500 rpm, is bombarded with ion beams. For this a plurality of wafers are normally arranged on a rotary plate, as is described in U.S. Pat. No. 4,745,287.
Further processing steps with rotating wafers relate to the washing of the wafer (xe2x80x9cspin rinsingxe2x80x9d) similarly as in xe2x80x9cspin etchingxe2x80x9d, in which the wafer is charged with a cleansing liquid, e.g. with water of highest purity. The drying of the wafer is also possible in this manner: Liquid residues are hurled outwards by centrifugal forces (xe2x80x9ccentrifugal wafer dryerxe2x80x9d), see e.g. U.S. Pat. No. 4,300,581.
Although only a selected number of processes or process steps respectively have been described above, there are numerous further process steps or processing steps respectively of this kind which are carried out in a process chamber with rotating wafers. In this, various mediaxe2x80x94among them radiation is also to be understoodxe2x80x94such as liquids, suspensions with solids, gases and vapours, electromagnetic fields, ion beams etc. are applied to the wafer as a rule with the help of applicators such as nozzles and nozzle systems (heads with a large number of nozzles), tube systems, radiation sources, electrodes, heating elements and heat radiators.
In this the wafer is at least individually rotated, or else a plurality of wafers are rotated in common with the help of a corresponding rotatable holder apparatus. This holder apparatus is designated in the following as a rotary head for the sake of simplicity. The rotary head, which holds and rotates the wafer, is often driven via a rotating shaft most often from below, sometimes also from above. In this the rotating shaft is introduced into the inner space of the process chamber via a seal from below or from above. The drive motor is located as a rule outside the inner space of the process chamber in order to keep the inner space of the process chamber free from contaminations (clean room conditions) and to protect the motor against corrosion.
The applicators (nozzles, nozzle systems, tube lines, electrodes, radiation sources, etc.) are necessarily located above or below the rotary head. Only in exceptional cases (application of gases) is it possible to treat the wafer from both sides. In every case, however, the driving of the rotary head from below or from above represents a restriction in regard to the arrangement of the applicators.
This manner of driving and journalling the rotary head also represents an additional restriction for the supplying of the wafer or wafers respectively. The wafer (the wafers) canxe2x80x94when the rotary head is driven from belowxe2x80x94not be supplied from below. The supplying from above is mostly also not possible due to the arrangement of the applicators, so that in such cases the wafer can practically only be supplied from the sidexe2x80x94stated more precisely, from laterally above the rotary head. This makes the centering of the wafer considerably more difficult and in addition limits the freedom of the arrangement of the applicators because, of course, the free access from the side up to the centre of the rotary head must be ensured.
The object of the invention is thus to propose a process chamber in which different processing steps can be carried out in the manufacture of semiconductors, in which process chamber the named spatial restrictions with respect to the arrangement of applicators are not present. The supplying of the wafer should also be more simply possible than in known process chambers.
This object is satisfied by a process chamber such as is characterised by the features of the independent patent claim. In particular, a rotationally drivable rotary head is arranged in the process chamber which serves as a holder for a substantially disc-shaped object to be processed, e.g. for a wafer. Furthermore, at least one applicator is provided. in the process chamber for the provision of a medium which acts on the object to be processed. Arranged radially around the rotary head, means are provided for the journalling and the driving of the rotary head. This radial arrangement enables, depending on the arrangement of the applicators, the wafer to be supplied centrally from below or from above and thus facilitates a centering of the wafer.
Furthermore, it is possible through the radial arrangement of the means for the journalling and for the driving around the rotary head to process the introduced wafer both from above and from below without this being excluded by a drive shaft or the like.
The means for the journalling and the driving of the rotary head are preferably formed in such a manner that they journal and drive the rotary head without contact; in particular these means comprise a magnetic bearing/drive unit, which is often designated as a xe2x80x9cbearing-free motorxe2x80x9d.
In this the magnetic bearing/drive unit can comprise a stator which is arranged outside the housing of the process chamber and the rotary head can be arranged inside the housing, with the (non-magnetic) housing wall forming a tubular gap, which seals the inner space of the housing against the outside. Through this, on the one hand, the gap between the rotary head and the stator can be kept small (which has a greater stiffness of the bearing as a result when the flux is the same); on the other hand, a possibly corrosive medium always remains in the inner space of the housing and can not penetrate to the outside.
In an exemplary embodiment of the process chamber in accordance with the invention all six degrees of freedom of the rotary head, namely the two degrees of freedom of the displacement in the bearing plane, the axial displacement, the two degrees of freedom of tilting and the rotation, can be actively controlled. This enables a very precise positioning of the rotary head in regard to each of the degrees of freedom, but is naturally more complicated and expensive from the point of view of the electronics than the two following variant embodiments.
In one of these variations two degrees of freedom of the rotary head can be actively controllable, namely the two degrees of freedom of the displacement in the bearing plane, whereas the other four degrees of freedom are passively stabilised. This reduces the cost and complexity in the electronics; in return, however, the axial displacement, the rotation and the two degrees of freedom of the tilting are merely passively stabilised. As concerns the axial displacement and the tilting of the rotary head, this means that a rotary head which has been deflected out of its passively stabilised position with respect to one of these degrees of freedom is brought back into its stable position through reluctance forces as long as the deflection is not greater than a threshold value. When this threshold value is exceeded, however, a stable journalling of the rotary head is no longer provided. As concerns the rotation, this means that the rotary head can be e.g. magnetically coupled to the bearing stator and this bearing stator itself is designed to be rotatable. As a result of the magnetic coupling, then, the rotary head is co-rotated when the bearing stator is rotated.
In another, particularly preferred variant, three degrees of freedom of the rotary head can be actively controlled, namely the two degrees of freedom of the displacement in the journalling plane and the rotation, whereas the other three degrees of freedom, namely the axial displacement and the two degrees of freedom of the tilting are passively stabilised. Through this, on the one hand, the cost and complexity of the electronics is still comparatively low; on the other hand, however, the stator need not be designed to be rotatable, but rather the rotary head can be driven rotationally by means of a rotary field.
In an advantageous embodiment of the process chamber in accordance with the invention the rotary head is designed in such a manner that the object to be processed can be connected outside the inner space of the process chamber to the rotary head in such a manner that it is held by the latter. The object to be processed can then be brought into the inner space of the process chamber together with the rotary head. This has the advantage that a precise positioning of the object, e.g. of the wafer, relative to the rotary head can take place outside the process chamber, where the rotary head is better accessible. In addition it is possible in this manner to connect the wafer only a single time very precisely to the rotary head and then to pass on the unit formed by the rotary head and the wafer from one processing station to another processing station without it being necessary to position the wafer anew on another rotary head. This can take place within a system of process chambers which are connected by locks in order that the clean room conditions are not violated in the mean time, with the degree of cleanliness continually increasing in successive process chambers.
The rotary head can be designed in such a manner that the object held by the rotary headxe2x80x94e.g. the waferxe2x80x94can be charged from both sides by a medium which is provided by the applicator. This is advantageous in so far as for example both sides of the wafer can be processed at the same time. The processing of the two sides can however also take place sequentially. In any case it is possible to process both sides of the wafer without it being necessary to rotate the wafer for this, such as is the case when itxe2x80x94as in a large number of the apparatuses from the prior art discussed in the introductionxe2x80x94lies in contact on a rotary plate with a drive shaft.
The rotary head can be designed substantially in the shape of a ring for this. In the interior of the rotary head however a disc with passage channels can also be fitted in, with the object to be processed, e.g. the wafer, being held at a distance from this disc by the rotary head. This disc can form a nozzle system through which the wafer can be charged e.g. with vapours or gases.
In another embodiment of the process chamber the rotary head can be designed substantially in the shape of a disc and the object to be held can be held in a central region of the rotary head. The rotary head is designed to have a declination in the peripheral region around this central region in order that a liquid which is applied to the object to be processed, and which flows outwardly over the object to be processed when the rotary head is rotationally driven, can run off over the peripheral region of the rotary head.
In a further development of this variant the rotary head has, around the peripheral region which is designed with a declination, a tub for the liquid which has passage openings at its base for the liquid which is caught in the tub. This variant is advantageous in so far as thereby the air gap between the rotary head and the stator can be kept small; on the other hand, the liquid need not also run off through this gap, which is small as it is. Instead, the liquid can be caught in the tub and can run off through the passage openings in the base of the tub.
In a further exemplary embodiment of the process chamber the rotary head which serves for the object to be processed, e.g. for the wafer, has means with the help of which a depression is conducted to the object to be processed which sucks the object to be processed firmly onto the rotary head. This can preferably even take place outside the inner space of the housing of the process chamber so that the wafer can be positioned on the rotary head at an easily accessible location and then sucked on. Once sucked on, the rotary head together with the sucked on wafer is then transported into the inner space of the housing of the process chamber. For the production of a depression at the rotary head which serves as a holder, for example a vacuum pump can be provided, which is preferably fed inductively.